BACKPORT: FROMGIT: sched/core: Remove ifdeffery for saved_state

In preparation for freezer to also use saved_state, remove the
CONFIG_PREEMPT_RT compilation guard around saved_state.

On the arm64 platform I tested which did not have CONFIG_PREEMPT_RT,
there was no statistically significant deviation by applying this patch.

Test methodology:

perf bench sched message -g 40 -l 40

Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

(cherry picked from commit fa14aa2c23d31eb39bc615feb920f28d32d2a87e
 https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git

 sched/core)
Bug: 292064955
Bug: 304294320
Change-Id: I9c11ab7ce31ba3b48b304229898d4c7c18a6cb2c
[eberman: Use KABI reservation to preserve CRC/ABI of struct task_struct and
 preserved raw_spin_(un)lock instead of new guard(...) syntax in task_state_match]
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
(cherry picked from commit 457e6569)